U.S. Pat. No. 4,135,851 to R. C. Bill and L. P. Ludwig discloses several seals using various compliant backing materials, including a low density sintered metal, which effectively reduce operating thermal stresses during steady operating conditions and transient thermal conditions. Because of the open porosity of sintered metals, oxidation of the metal does not lead to swelling and distortion. However, brazed bonding attachments are required with the sintered metal backings.
U.S. Pat. No. 4,075,364 to Panzera describes various methods for securing a ceramic layer to a low modulus structure. Elbert et al U.S. Pat. No. 3,975,165 is directed to a graded metal-to-ceramic abradable seal which is produced by laying up layers in wet paste form and then drying.
Graded metal ceramic layers have also been applied by plasma spray deposition. The problems encountered with graded coatings are discussed in column 1 of U.S. Pat. No. 4,055,705 to Stecura et al.